Apparatus for continuous production of crimped filaments



Oct. 10, 1967 G. SCHATZ ETAL 3,345,719

APPARATUS FOR CONTINUOUS PRODUCTION OF CRIMPED FILAMENTS Filed June 22, 1964 2 Sheets-Sheet 1 FIGI ATT'YS Oct. 10, 1967 5. SCHATZ ETAL 3,345,719

APPARATUS FOR CONTINUOUS PRODUCTION OF CRIMPED PILAMENTS Filed June 22, 1964 v 2 Sheets-Sheet 2 FIG. 2

FIG. 3

64 65 48 INVENTORS: GUNTHER SCHATZ I 66 M HERMAN QEMEINHARDT 3 HANS BRUCHER ATT 'YS United States Patent 3,345,719 APPARATUS FOR CONTINUOUS PRODUCTION OF CRIMPED FILAMENTS Giinther Schatz and Hermann Gemeinhardt, Elsenfeld,

and Hans Briicher and Otto Jurisch, Klingenberg, Germany, assignors to Vereinigte Glanzstolf-Fabriken A.G., Wuppertal-Elberfeld, Germany Filed June 22, 1964, Ser. No. 378,488 Claims priority, applicatign Gtgrmany, June 24, 1963,

4,21 7 Claims. (Cl. 28-1) ABSTRACT OF THE DISCLOSURE Apparatus for crimping tow or yarn having (a) a pair of juxtapositioned feed rolls; (b) a hollow member with a short axial passage defining a short, preferably cylindrical, compression throat adjacent the rolls and a lower compression chamber having a cross-sectional area about 1.2 to 2 times the cross-sectional area of the throat and a length about 2.5 to 7 times the length of the throat; (c) a pivotable shutter adapted to open and close the lower end of the compression chamber; (d) means biasing the shutter toward closed position; (e) a hollow member at the lower end of the compression chamber defining a buffer space (preferably rectangular in transverse cross section) below the compression chamber; (f) a pivota-ble second shutter at the lower end of the buffer space; (g) an electrical switch activated by movement of the second shutter, preferably with means biasing the second shutter toward closed position at a bias load of at least 20% of the crimped yarn or tow in the buffer space and about 210% of the bias load on the first mentioned shutter; (g) a winding spool rotatably driven by a multi-speed electric motor for drawing the crimped yarn or tow from said bulfer space, and means responsive to movement of said second shutter for alternating the speed of said motor between a faster speed when said second shutter is open and a slower speed when said shutter is closed; and (h) a rounded rib on a wall of the buffer space opposite the hinged side of the side shutter against which swinging end of second shutter abuts.

This invention, in general, relates to apparatus for producing crimped filaments, such as crimped yarns, crimped tows of endless filaments, and the like. More specifically,

apparatus of the invention pertains to stuffing box-type crimping wherein a straight or uncrimped yarn or tow is fed into and initially crimped in a short compression throat, forced into. a compression chamber having a larger cross-section than the cross-section of said compression throat, periodically discharged from said compression chamber into a buffer space and periodically withdrawn from said buffer space by a winding device synchronously operated at alternating winding speeds.

Production of crimped yarn or filaments in a stufiing box or compression chamber, broadly, is known in the art. Straight yarn or filament is forced by a pair of delivery rolls into a chamber with a round or rectangular cross-section. The chamber may be closed at its opposite end with a shutter or the like. The yarn or filament is undulated and compressed in the compression chamber or stutfing ibox until the interior pressure in the chamber is sufficient to open the shutter or the like. All heretofore known compression, crimping processes are based on this general principle of operation.

In some processes, the yarn or filament is pressed into the compression chamber in the above described manner. After emergence therefrom, it is deposited without any or with little tension imparted to the yarn or filament.

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After the container becomes filled, the crimped yarn or filament is put in a fixing or setting oven, wherein the crimping impressed on the yarn or filament is fixed so that the yarn or filament retains its crimped set.

There are also known processes for continuous crimping, in which the yarn or filament is drawn off either at a predetermined, constant speed or at alternating higher and lower speeds. In the latter case, the movements of the shutter or like closing device are utilized to switch the energization of the electric motor for the winding spool in brief cycles between a speed of rotation considerably below the mean draw-oif and a speed considerably above the mean draw-off speed. The two speeds average the correct, mean, draw-off speed.

It has been noted, however, that processes operated in the above described manner do not meet the demands for uniformity of crimping, especially in processes where the yarn or filaments are crimped continuously. One of the problems with these prior art processes is apparently attributable to the fact that a considerable portion of the pressure in the compression chambers or stuffing boxes is attributable to friction between the undulated, crimped yarn or filament and the walls of the compression chamber or stufling box. This component of the pressure may be as much as 80% of the total pressure when the crimped yarn or filament is static. After reaching the limiting static pressure, the crimped yarn or filament packed in the crimping chamber or stuffing box begins to move. The sliding friction at this stage is considerably less than static friction, and the effective interior pressure in the chamber or box diminishes relatively severely. As a result, a considerably greater portion of the material is ejected from the chamber or box than would be the case had a more uniform interior pressure been maintained.

A compression chamber structurally adapted to provide low wall friction is not, in itself, the best approach to solving the problem of nonuniformly crimped yarn or filaments. For example, a compression chamber of the aforesaid character and having a shutter or the like operable on "build up of interior pressure in the compression chamber and further including a switch for speed control of the winding spool motor operable by the opening and closing of the shutter does not completely solve the problem. This is because the yarn or filament packed in the compression chamber are thrust irregularly out of the compression chamber exit. The shutter movement necessary for operation of the switching results in a variably high filling of the compression chamber. The irregular thrusting of the crimped yarn or filament from the chamber exit shifts the compression or bending points of the yarn or filament back and forth with respect to I the distance from the contact point between the two feed rolls. This results in relatively great differences in length of crimping yarns.

Attempts have been made in various ways to eliminate the disadvantage of nonuniform crimping. It has been proposed that the feed rate of the uncrimped yarn or filament and the draw-off speed of the crimped yarn or filament be set at a fixed ratio and left unchanged. The fixed amount of crimped yarn or filament is accumulated after exit from the compression chamber in the case of a correctly-set crimping operation. The exit of the accumulated, crimped yarn or filament points measured and used for operation of a servomotor to keep the yarn or filament accumulation relatively constant. It is readily recognized that, however, it is impossible to avoid fluctuations in the size of the crimped yarns because the appearance of such fluctuations or deviations in such crimping system. Experience has shown that the initial setting of the device to give a uniform crimping is not attainable in actual practice and that such devices, therefore, must depend upon the correction of irregularities which have already occurred in the crimping operation.

Still another type of noncompression chamber is one in which the yarn or filament conveyed upwardly and in which, instead of a weight-loaded shutter, a gear wheel is provided at the chamber exit. The gear wheel has sawteeth, the steeply pitched teeth of which are pointed opposite the running direction of the yarn or filament. The wheel is braked with an adjustable torque against the running direction of the yarn or filament. In this device it is not possible to eliminate the known disadvantages because, in addition to wall friction with its alternation between static and sliding values, there is also involved the friction brake for the gear wheel. Other problems stem from the reliable regulation of the draw-off and from the space above the compression chamber, closed off by the gear wheel. The drawing off of the crimped yarn or filament took place directly out of the compression chamber, resulting in the previously described disadvantages. It has now been found, in accordance with the invention, that a uniform crimping of yarn or filament can be achieved essentially by the combination of two measures. First, the effect of the wall friction between the wall of the compression chamber and the filament crimped therein under pressure of the feed of filament by the feeding mechanism must be kept at a low proportion to the total resistance of the compression chamber on the crimped filament or yarn. The proportion of the wall friction to the wall resistance should be kept below about 20%. Second, the crimping must be carried out so that draw-off of the crimped filament directly from the compression chamber must be avoided in order not to vary the degree of filling of the compression chamber by yarn or filament in an uncontrollable manner.

Briefly, the invention provides for the feed of uncrimped yarn or filament, preferably by opposed feed rolls, into a short compression throat. The compression throat preferably is round in transverse cross-section and has a diameter adapted to the delivery rolls. After the compression throat, in which the filament or yarn is crimped by continuous feed under pressure of the uncrimped yarn or filament by feed rolls, the crimped yarn or filament enters a compression chamber, at least the upper portion of which is preferably also round in transverse cross-section. This cross-section of the compression chamber is larger than the cross-section of the compression throat, i.e., about 1.2 to 2 times the cross-section of said throat. The enlarged cross-section of the compression chamber is utilized to reduce wall friction between the compression chamber and the crimped yarn or filament to a low value. It has been observed that good results can be achieved within a range in which the ratio of the throat diameter to the diameter of the immediately following, upper portion of the compression chamber is between about 1:1.1 and 1:2, respectively. The length ratio of the length of the compression throat and the compression chamber should be between about 112.5 and 1:7, preferably between 1:35 and 1:5, respectively.

By these measures, the yarn or filament bent in the compression throat in undulating fashion enters the enlarged compression chamber having on its exit end a shutter with means biasing the shutter toward closed position. The shutter preferably is a diagonally extending plate with pivot means, and the shutter bias is preferably a Weight biasing the shutter toward closed position. The shutter bias is the principal component of force resisting discharge of the crimped filament from the compression chamber. As a result, the crimped filament or yarn emerges uniformly from the compression chamber and has, as a consequence, a uniform crimping.

Following the compression chamber, there is provided a hollow space, i.e., an axial passage, in which the crimped yarn or filament is accumulated upon discharge from the compression chamber. The crimped yarn or filament accumulates in the buffer space, closed at its exit end by a second shutter, until the weight of the accumulated crimped yarn or filament in the buffer space opens the second shutter. When the second shutter opens, it actuates a microswitch operatively connected in the electrical circuit of multi-speed drive motor driving the takeup spool or winding tube for the crimped yarn or filament. In this arrangement, the switch actuated by the second shutter can easily be adjusted so that the buffer space following the compression chamber remains essentially constantly filled to a predetermined degree. The level of filling fluctuates only slightly.

With respect to the loading of the two shutters, it has been found that the degree of crimping is dependent only on the pressure build-up in the compression chamber and compression throat. The loading of the second shutter is kept at a low value so that retroactive effect into the compression chamber is avoided as far as possible. This keeps the mechanism from operating in a manner Wherein, in effect, the crimped yarn or filament is drawn directly from the compression chamber. The pressure applied by the second shutter on the yarn or filament movement therethrough should be at least about equal to 20% of the weight of the yarn or filament mass lying in the buffer space above the second shutter, and it must be, at most, about 10%, if possible not more than about 2% to 5%, of the bias load on the first shutter for the compression chamber.

It is advantageous in some cases, for the increase of torque acting on the second shutter under given loading conditions, to provide an arcuate bend at the free edge of the second shutter to move the engagement point of the yarn or filament lying on the shutter downwardly as far as possible. Also, it is preferred that the second shutter should strike a rib or lug on the wall opposite to the wall on which the second shutter is hinged. This structure aids in preventing slippage of the crimped yarn or filament from the buffer space, even in the case of relatively widely opened shutters. This lug can be formed integrally in the wall of the buffer space, but it can also be a cylindrical rod, which is seated and secured in a groove in said wall.

The invention, and its objectives and advantages, will be further appreciated from the following description of the preferred embodiment of the invention, which is illustrated in the drawings wherein:

FIG. 1 is a side elevation, partly in cross-section, of a device for continuous crimping and constructed in a manner previously described;

FIG. 2 is a schematic view of a crimping operation from feed of uncrimped filament to winding of the crimped filament and utilizing the crimped device of FIG. 1, and

FIG. 3 is a schematic view of a circuit diagram for the electrical circuit of the winding tube drive motor and the microswitch operated by shutter movement.

Referring to the drawings shown in FIG. 1, uncrimped yarn or filament 10 is gripped by the nip of opposed, oppositely rotating feed rolls 11 and 12 and fed into the crimping device 13 below the feed rolls. The crimping device 13 comprises a hollow member providing axial passage therethrough. The upper portion of the device 13 has a compression throat 14, preferably round in transverse cross-section with its upper, open end closely fitted with relation to the feed rolls 11 and 12 and extending as far as possible toward the nip of the feed rolls. Following the short, compression throat 14 is a compression chamber 15 also preferably round in transverse cross-section and larger in diameter or cross-sectional area than the diameter or cross-sectional area of the compression throat 14, as previously described. The axial passage 16 through compression device 13 thus provides the compression throat 14 and compression chamber 15.

The lower end of the compression device 13 is fixedly mounted in the upper end of the member 17 having an axial passage therethrough and communicating with the lower end of compression chamber 15. The axial passage preferably is rectangular in cross-section, the upper portion 18 of which lies over shutter 19.

The shutter 19 comprises a diagonally extending shutter plate 21 lying diagonally across and substantially filling the axial passage in the member 17. In the wall 22 of the member 17 is a cut out segment 23, along the upper edge of which extends the pin 24. The hub 25 of the shutter 19 is pivotally mounted on the pin 24 whereby the shutter plate 21 is pivotable. An arm 26 extends radially from hub 25 outwardly from the member 17. The arm 26 has an upwardly extending pin 27 on which is removably seated a hollow, cylindrical weight 28. The torque arm provided by arm 26 and weight 28 constitutes a bias means for biasing the shutter plate 21 toward closed position to close off the compression chamber 15 and the extension thereof defined by the upper portion 18 in member 17.

The portion 29 of member 17 below the shutter plate 21 defines a hollow, buffer space in which crimped yarn is accumulated after the latter has passed the shutter plate 21. During operation of the crimping apparatus, crimps 31 are formed initially in the throat 14 in continuous fashion. Filament crimps 32, which have passed from float 14 into the compression chamber 15, are pushed against shutter plate 21 by pressure of continuous feed of filament to and through compression throat and compression chamber. Wall friction between the filament portion having crimps 32 in the compression chamber 15 is at a low value. The pressure operating against the upper surface of the shutter plate 21 is resisted primarily by the bias of torque arm 26 and weight 28. When this pressure opens the shutter 19 sufiiciently to allow filament to pass out of the compression chamber past the shutter plate, it accumulates in the buffer space 29, which preferably is of rectangular cross-section.

The lower part of the buffer space 29 has a second or regulating shutter 33 comprising a shutter plate extending diagonally downwardly across the lower end of the buffer space 29. The upper edge of the shutter 33 is pivotally mounted in the upper edge of the space 35 of wall 36 by the pin 34. The lower, free edge of the shutter plate preferably seats against a rib 37 having a rounded contour. In the illustrated case, the rib 37 is a cylindrical rod fixedly seated in a semicylindrical, transversely extending groove in the lower edge of wall 22.

The regulating shutter 33 has only a light spring bias urging it to closed position, i.e., the light bias of the actuator arm 43 of microswitch 42. The bias urging shutter 33 toward closed position is substantially less than the bias on shutter 19, as has ben previously described.

Microswitch 42 is positioned adjacent the second shutter 33. The microswitch is illustrated diagrammatically in the drawings inasmuch as the structure of the microswitch per se does not constitute a part of the invention. Many known microswitches are suitable for the purpose herein described. Microswitch 42 has an actuator arm 43 operatively connected to the switching component of the microswitch. The outer end of the actuator arm 43 may have a roller mounted thereon, which roller bears against the under surface of the shutter 33.

The microswitch has at least two switching positions, one of which is closed when shutter '33 is in closed position as shown in FIG. 1. The other switching position is closed when the shutter 33 opens a predetermined amount.

The arm 43 of the microswitch may be resiliently biased so that it presses the shutter toward closed position. In such case, it is preferred that there be provided with the resilient bias on the arm 43 means for adjusting the degree of bias so that the bias on the shutter 33 is adjustable.

The lower, free edge of the shutter 33 preferably is curved to present the convex surface facing the rib 37. The advantage of such structure has been described previously with regard to keeping the portion 46 of the crimped filament from falling out of the lower end of the buffer space even when the shutter 33 is in a relatively widely opened position.

The microswitch 42 is electrically connected by a circuit 47 with the electrical circuit for the motor 48. The motor 48 is a multi-speed electric motor, the speed-controlling circuitry of which is controlled by the microswitch 42. This allows the motor 48 to drive the winding 49 on the rotatably driven winding tube or spool 50' at least two different rates of rotation. The slower rate of rotation occurs when shutter 33 is closed and the faster rate of rotation occurs when shutter 33 moves a predetermined amount away from closed position under the urging of the weight of accumulated yarn or filament in buffer space 29.

The over-all crimping operation is illustrated diagrammatically in FIG. 2 wherein uncrimped yarn or filament is drawn off wound spool 51 through a thread brake of known construction and over a roller or bar 53. The yarn or filament passes over or around a heating plate 54 on which yarn or filament 1-0 is heated at the desired tempertaure. The yarn then passes through a feed tube 55 into the nip of the draw rolls 11 and 12. The yarn or filament is forced through and crimped in the device previously described and exits from the lower end of the buffer space 29 under the control of the shutter 33, which is drawn onto the winding 49 at rates depending upon the position of the shutter 33, as previously described, over a series of deflection rollers 56, around the roller 57 of a finishing bath 58 and over a deflection roller 59 onto the winding 49 of the crimped filament.

The two-speed control of motor 48 may be achieved by using a variable speed motor, the rate of revolution of which is variable in accord with the frequency of the alternating current supplied thereto. The circuit of FIG. 3 shows a simple type of circuit for controlling the speed of motor 48 through microswitch 42. Current of one frequency is supplied through current main 60 and current of another frequency is supplied through current main 61 to switch contact points '63 and 62, respectively. Movable switch element 64 is moved between these points by the link 65, which in turn is linked to actuator arm 43. The particular current supplied to motor 48 via switch element 64 and current main 66 depends upon which of contact points 62 and 63 is contacted by the movable element 64. The microswitch is oriented so that 'the current frequency which drives the motor 48 at the faster speed is supplied thereto when the shutter 33 is open and the current frequency which drives the motor at the slower speed is supplied thereto when shutter 33 is closed or approximately closed. If desired, the current mains 60 and 61 can be connected to a switch-over device such as a relay or relays (not shown), which relay is connected by a separate circuit to microswitch 42 whereby the current for motor 48 passes through the relay switches and not the microswitch 42. The relay switches are opened and closed in response to the opening and closing of the switch element 64 and contact points 62 and 63.

The yarn or filament is continuously drawn from the buffer space 29 at one or the other speed. The shutter 33 constantly moves back and forth during the process. With the bias of actuator arm 43 on the shutter 33 in proper balance to achieve the correct mean draw-off speed of the crimped filament or yarn from the buffer space 29, the buffer space remains filled, within narrow limits, to the desired degree and thereby prevents retroaction against the functioning of the crimping operation proper in the compression throat and compression chamber.

A specific example of the crimping process of the invention follows. Nylon 66 yarn (linear polycondensate of adipic acid and hexamethylene diamine) having the denier 1000/ 72/0, Y profile, is looped about the heating plate 54, which is maintained at about 160 C. The yarn is fed by feed rolls 11 and 12 to the crimping device illustrated in the drawings at about 600 meters per minute. The crimped yarn is drawn from the buffer space, under the control of shutter 33 as aforedescribed, at a faster speed of 570 meters per minute and a slower speed of 470 meters per minute. The load on shutter 21 is 300 grams.

The invention is hereby claimed as follows:

1. Apparatus for crimping tow or yarn comprising a pair of juxtapositioned feed rolls adapted to feed said tow or yarn therebetween, a hollow member with an axial passage therein, said axial passage defining an upper short, compression throat adjacent said rolls and a lower, compression chamber having a cross-sectional area which is about 1.2 to 2 times the cross-sectional area of said throat, and having a length about 2.5 to 7 times the length of said throat, a pivotable shutter at the lower end of said compression chamber by which the lower end of said compression chamber is opened and closed, means biasing said shutter toward closed position, a hollow member with an axial passage communicating with the lower end of said compression chamber and defining a bufi'er space below sad compression chamber, and a pivotable second shutter at the lower end of said buffer space adapted to pivot between open and closed position.

2. Apparatus for crimping tow or yarn comprising a pair of juxtapositioned feed rolls adapted to feed said tow or yarn therebetween, a hollow member with an axial passage therein, said axial passage defining an upper short, compression throat adjacent said rolls and a lower, compression chamber having a cross-sectional area which is about 1.2 to 2 times the cross-sectional area of said throat, and having a length about 2.5 to 7 times the length of said throat, a pivotable shutter at the lower end of said compression chamber by which the lower end of said compression chamber is opened and closed, means biasing said shutter toward closed position, a hollow member with an axial passage communicating with the lower end of said compression chamber and defining a bufier space below said compression chamber, a pivotable second shutter at the lower end of said butter space adapted to pivot between open and closed position, an electrical switch and means responsive to movement of said second shutter for actuating said swich.

3. Apparatus for crimping tow or yarn comprising a pair of juxtapositioned feed rolls adapted to feed said tow or yarn therebetween, a hollow member with an axial passage therein, said axial passage defining an upper short, compression throat adjacent said rolls and a lower, compression chamber having a cross-sectional area which is about 1.2 to 2 times the cross-sectional area of said throat, and having a length about 2.5 to 7 times the length of said throat, a pivotable shutter at the lower end of said compression chamber by which the lower end of said compression chamber is opened and closed, means biasing said shutter toward closed position, a hollow member with an axial passage communicating with the lower end of said compression chamber and defining a buffer space below said compression chamber, a pivotable second shutter at the lower end of said buffer space adapted to pivot between open and closed position, second bias means biasing said second shutter toward closed position at a bias load of at least 20% of the weight of the crimped yarn or tow in said bufier space when said apparatus is in operation and about 2% to of the bias load of said first-mentioned bias means.

4. Apparatus as claimed in claim 3 wherein said second shutter is hinged along one edge thereof on one side of said buffer space, and a rounded rib projecting from the wall of the opposite side of said buffer space, against 8 which rib the opposite edge of said second shutter abuts when said shutter is closed.

5. Apparatus for crimping tow or yarn comprising a pair of juxtapositioned feed rolls adapted to feed said tow or yarn therebetween, a hollow member with an axial passage therein, said axial passage defining an upper short, compression throat adjacent said rolls and a lower, compression chamber having a cross-sectional area which is about 1.2 to 2 times the cross-sectional area of said throat, and having a length about 2.5 to 7 times the length of said throat, a pivotable shutter at the lower end of said compression chamber by which the lower end of said compression chamber is opened and closed, means biasing said shutter toward closed position, a hollow member with an axial passage communicating with the lower end of said compression chamber and defining a buffer space below said compression chamber, and a pivotable second shutter at the lower end of said buffer space adapted to pivot between open and close-d position, said compression throat and upper portion of said compression chamber being cylindrical, and the lower portion of said compression chamber and said butter space being rectangular in transverse cross-section.

6. Apparatus for crimping tow or yarn comprising a pair of juxtapositioned feed rolls adapted to feed said tow or yarn therebetween, a hollow member with an axial passage therein, said axial passage defining an upper short, compression throat adjacent said rolls and a lower, compression chamber having a cross-sectional area which is about 1.2 to 2 times the cross-sectional area of said throat, and having a length about 2.5 to 7 times the length of said throat, a pivotable shutter at the lower end of said compression chamber by which the lower end of said compression chamber is opened and closed, means biasing said shutter toward closed position, a hollow member with an axial passage communicating with the lower end of said compression chamber and defining a buffer space below said compression chamber, a pivotable second shutter at the lower end of said buffer space adapted to pivot between open and closed position, a winding spool rotatably driven by a multi-speed electric motor for drawing the crimped yarn or tow from said butter space, and means responsive to movement of said second shutter for alternating the speed of said motor between a faster speed when said second shutter is open and a slower speed when said shutter is closed.

7. Apparatus for crimping tow or yarn comprising a pair of juxtapositioned feed rolls adapted to feed said tow or yarn therebetwen, a hollow member with an axial passage therein, said axial passage defining a compression throat adjacent the rolls and a lower compression chamber, a pivotable shutter at the lower end of said compression chamber by which the lower end of said compression chamber is opened and closed, means biasing said shutter toward closed position, a hollow member with an axial passage communicating with the lower end of said compression chamber, a pivotable second shutter at the lower end of said butler space adapted to pivot between open and closed position, a winding spool rotatably driven by a multi-speed electric motor for drawing the crimped yarn or tow from said buffer space, and means responsive to movement of said second shutter for alternating the speed of said motor between a faster speed when said second shutter is open and a slower speed when said shutter is closed.

References Cited UNITED STATES PATENTS 2,846,729 8/1958 Sonnino 1966 2,865,080 12/1958 Hentschel 281 3,022,545 2/1962 Wylde 264-168 X 3,200,466 8/1965 Duga et al. 28-1 MERVIN STEIN, Primary Examiner.

L. K. RIMRODT, Examiner. 

1. APPARATUS FOR CRIMPING TOW OR YARN COMPRISING A PAIR OF JUXTAPOSITIONED FEED ROOLS ADAPTED TO FEED SAID TOW OR YARN THEREBETWEEN, A HOLLOW MEMBER WITH AN AXIAL PASSAGE THEREIN, SAID AXIAL PASSAGE DEFINING AN UPPER SHORT, COMPRESSION THROAT ADJACENT SAID ROLLS AND A LOWER, COMPRESSION CHAMBER HAVING A CROSS-SECTIONAL AREA WHICH IS ABOUT 1.2 TO 2 TIMES THE CROSS-SECTIONAL AREA OF SAID THROAT, AND HAVING A LENGTH ABOUT 2.5 TO 7 TIMES THE LENGTH OF SAID THROAT, A PIVOTABLE SHUTTER AT THE LOWER END OF SAID COMPRESSION CHAMBER BY WHICH THE LOWER END OF SAID COMPRESSION CHAMBER IS OPENED AND CLOSED, MEANS BIASING SAID SHUTTER TOWARD CLOSED POSITION, A HOLLOW MEMBER WITH AN AXIAL PASSAGE COMMUNICATING WITH THE LOWER END OF SAID COMPRESSION CHAMBER AND DEFINING A BUFFER SPACE BELOW SAD COMPRESSION CHAMBER, AND A PIVOTABLE SECOND SHUTTER AT THE LOWER END OF SAID BUFFER SPACE ADAPTED TO PIVOT BETWEEN OPEN AND CLOSED POSITION. 